Air bags for motor vehicles are known and have been used since the 1970's. The first type of bag was placed in the steering wheel and is conventionally referred to as the driver side air bag. A typical material from which the driver side air bags have been made is a neoprene coated nylon fabric material.
The neoprene material is useful because it acts as an impermeable insulation to the inflation medium. This inflation medium is generally a nitrogen gas which is generated from a gas generator or inflator and arrives into the bag at relatively warm temperatures. Thus, the neoprene substantially prevents the permeation of the fabric by the hot gas to thus avoid burns to the passenger. In addition to acting as an insulation shield and as a membrane which prevents gas from passing therethrough, the neoprene also gives additional integrity to the nylon fabric substrate.
In order to improve upon the passive restraint systems of automobiles, air bags are now being considered for use on the passenger side, as well as the driver side, in combination with three point seat belts for maximum safety to the vehicle occupants. On the passenger side, it is not necessary to construct the air bag of a coated fabric because cooler gas is introduced into the bag from the inflator. In addition, the bag on the passenger side is generally longer and of a different shape so that it retains the inflation gas for a longer period of time, with the gas cooling during the inflation. Accordingly, the use of a coated fabric is not necessary for a passenger side air bag and would not be preferred because of the additional cost considerations.
Therefore, passenger side air bags are generally made of an uncoated fabric or a very lightly coated fabric. Proposals have been made for preparing nylon fabrics which are uncoated but have sufficient permeability to retain the inflation gases therein. Such fabrics are described in U.S. Pat. Nos. 4,921,735 and 4,977,016.
When uncoated fabrics are used, however, there are problems involved with respect to the manufacture of such fabrics into an air bag. First of all, neoprene coated nylon fabrics are conventionally die cut to the proper shape before fabrication into the final air bag. It is difficult to die cut uncoated fabric because the fabric tends to fray in the areas where it is cut. Also, laser cutting can be used for preparing the desired shape of the fabric, but this is also undesirable for uncoated nylon fabric since, when a plurality of the fabrics are stacked upon each other and cut with the laser, they tend to fuse together in the area in which they are cut due to the melting of the nylon material. Furthermore, it is possible that an uncoated fabric could cause secondary injury due to permeation by hot gases through the fabric or by particulate matter which bypasses the inflator filter system. Thus, it would be desirable to have a fabric which includes a coating that sufficiently overcomes the aforementioned drawbacks of manufacture as well as to provide added safety to the passenger when the bag is deployed.
In today's market, polyurethane coated fabrics are utilized in a wide array of products and applications. Typically, polyurethane elastomers which are considered top of the line with respect to performance, include, for example, polytetramethylene glycol (polyether) polyurethanes and poly(butane adipates or hexane adipates) polyester polyurethanes. Of these polymers, the polyether polyurethanes exhibit good hydrolytic stability and low temperature properties but are generally poor for fuel resistance and oxidation resistance, while the polyester polyurethanes are tough with good abrasion resistance, oxidation resistance and fuel resistance, but not particularly resistant to hydrolysis. Still, at the present time the polyesters are generally considered to represent the best compromise of physical properties and chemical resistance of the various polyurethanes.
There are also a few polyurethanes based on polycarbonate polyols in the market. It is well known that these polycarbonate polyurethanes have very good hydrolytic stability and generally have good to very good resistance to other degradation forces; however, they are usually too hard, rigid and brittle for use in industrial coated fabrics.
Currently, high performance coated fabrics are based on polyester polyurethanes in order to meet the specifications currently in effect, but resistance to hydrolysis remains their weak point and represents a problem for these products. Thus, there is a desire for improved hydrolytic stability in a number of applications. A polyurethane having improved hydrolytic properties and sufficient elastomeric character to be useful in the manufacturing of industrial coated fabrics is also desirable and needed.
In addition, the construction of the fabric reinforcement is often important for increasing the strength of the coated fabric. The combination of a high performance polyurethane and fabric reinforcement provides a product which is flexible, tear resistant, resilient, foldable and tough.
Moreover, the fabric substrate is often manufactured in long wide rolls which are subsequently cut and trimmed for their end use. As noted above, uncoated fabrics fray during trimming and cutting operations. Coating the fabric material will often allow the fabric to be cut without the fabric fibers fraying but the prior art coatings often add unnecessary bulk and thickness to the fabric. There is a need for a process that will allow fabrics to be cut without the fabric fibers fraying and which does not add unnecessary bulk and thickness to the fabric. Additionally, there is a need for a coated fabric that is light weight, strong, flexible, foldable and impermeable so that the coated fabric may be used in the construction of air bags for either the passenger side or driver's side of an automobile.